Method for controlling a driveline in order to optimize fuel consumption

ABSTRACT

A method is provided to start a hybrid powertrain to optimize fuel consumption, wherein such hybrid powertrain comprises a combustion engine; a gearbox with input shaft and output shaft; a first planetary gear, connected to the input shaft and a first main shaft; a second planetary gear, connected to the first planetary gear and a second main shaft; first and second electrical machines respectively, connected to the first and second planetary gears; one gear pair connected with the first main shaft; and one gear pair connected with the second main shaft. The method comprising: ensuring that the moveable parts of each of the first and second planetary gears are respectively disconnected from each other; bringing the combustion engine to a predetermined engine speed (n ice ); and controlling the first and the second electrical machine in such a way that a desired torque (T Drv ) is achieved in the output shaft.

CROSS-REFERENCE TO RELATED REFERENCE(S)

This application is a national stage application (filed under 35 §U.S.C. 371) of PCT/SE15/050293, filed Mar. 17, 2015 of the same title,which, in turn claims priority to Swedish Application No. 1450326-2,filed Mar. 20, 2014 of the same title; the contents of each of which arehereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a method, vehicle, and computer programproduct to control a hybrid powertrain to optimize fuel consumption.

BACKGROUND OF THE INVENTION

Hybrid vehicles may be driven by a primary engine, which may be acombustion engine, and a secondary engine, which may be an electricalmachine. The electrical machine is equipped with at least one energystorage device, such as an electro-chemical energy storage device, forstorage of electric power and control equipment to control the flow ofelectric power between the energy storage device and the electricalmachine. The electrical machine may thus alternately operate as a motorand as a generator, depending on the vehicle's operating mode. When thevehicle is braked, the electrical machine generates electric power,which is stored in the energy storage device. This is usually referredto as regenerative braking, which entails that the vehicle isdecelerated with the help of the electrical machine and the combustionengine. The stored electric power is used later for operation of thevehicle.

A gearbox in a hybrid vehicle may comprise a planetary gear. Theplanetary gearbox usually comprises three components, which arerotatably arranged in relation to each other, namely a sun wheel, aplanetary wheel carrier and an internal ring gear. With knowledge aboutthe number of cogs in the sun wheel and the internal ring gear, themutual speeds of the three components may be determined duringoperation. One of the components of the planetary gear may be connectedwith an output shaft in a combustion engine. This component of theplanetary gear thus rotates with a rotational speed corresponding to therotational speed of the output shaft in the combustion engine. A secondcomponent in the planetary gear may be connected with an input shaft toa transmission device. This component of the planetary gear thus rotateswith the same rotational speed as the input shaft to the transmissiondevice. A third component in the planetary gear is used to achievehybrid operation, connected with a rotor in an electrical machine. Thiscomponent in the planetary gear thus rotates with the same rotationalspeed as the rotor of the electrical machine, if they are directlyconnected with each other. Alternatively, the electrical machine may beconnected with the third component of the planetary gear via atransmission that has a gearing. In this case, the electrical machineand the third component in the planetary gear may rotate with differentrotational speeds. The engine speed and/or the torque of the electricalmachine may be controlled steplessly. During operating times when theinput shaft to the transmission device must be provided with arotational engine speed and/or torque, a control device having knowledgeabout the engine speed of the combustion engine calculates therotational speed with which the third component must be operated, inorder for the input shaft to the transmission device to obtain thedesired rotational speed. A control device activates the electricalmachine, so that it provides the third component with the calculatedengine speed and thus the input shaft to the transmission device withthe desired rotational speed.

Depending on the design of the gearbox connected to the planetary gear,a torque interruption between the gear steps may be avoided. Often,however, separate and complex devices are required in the gearbox inorder to eliminate or reduce the torque interruption, so that aperception of stepless gear shifts is obtained.

By connecting the combustion engine's output shaft, the electricalmachine's rotor and the transmission device's input shaft with aplanetary gear, the conventional clutch mechanism may be avoided. Atacceleration of the vehicle, an increased torque must be delivered fromthe combustion engine and the electrical machine to the transmissiondevice, and further to the vehicle's driving wheels. Since both thecombustion engine and the electrical machine are connected with theplanetary gear, the largest possible torque delivered by the combustionengine and the electrical machine will be limited by one of these driveunits; i.e. the one whose maximum torque is lower than the second driveunit's maximum torque, having regard to the gearing between them. Incase the electrical machine's highest torque is lower than thecombustion engine's highest torque, having regard to the gearing betweenthem, the electrical machine will not be able to generate a sufficientlylarge reaction torque to the planetary gear, entailing that thecombustion engine may not transfer its highest torque to thetransmission device and further to the vehicle's driving wheels. Thus,the highest torque that may be transferred to the transmission device islimited by the electrical machine's strength. This is also apparent fromthe so-called planet equation.

Using a conventional clutch, which disconnects the gearbox's input shaftfrom the combustion engine during shifting processes in the gearbox,entails disadvantages, such as heating of the clutch's discs, resultingin wear of the clutch discs and an increased fuel consumption. Aconventional clutch mechanism is also relatively heavy and costly. Italso occupies a relatively large space in the vehicle.

In a vehicle, the space available for the drive arrangement is oftenlimited. If the drive arrangement comprises several components, such asa combustion engine, an electrical machine, a gearbox and a planetarygear, the construction must be compact. If there are additionalcomponents, such as a regenerative braking device, the requirements thatthe component parts must have a compact construction are even morestringent. At the same time, the component parts in the drivearrangement must be designed with dimensions that are able to absorb therequired forces and torque.

For some types of vehicles, especially heavy goods vehicles and buses, alarge number of gear steps is required. Thus, the number of componentparts in the gearbox increases, which must also be dimensioned to beable to absorb large forces and torque arising in such heavy goodsvehicles. This results in an increase of the size and weight of thegearbox.

There are also requirements for high reliability and high dependabilityof the components comprised in the drive device. In case the gearboxcomprises multi-plate clutches, a wear arises, which impacts thereliability and life of the gearbox.

At regenerative braking, kinetic energy is converted into electricpower, which is stored in an energy storage device, such asaccumulators. One factor impacting on the life of the energy storagedevice is the number of cycles in which the energy storage deviceprovides and extracts power to and from the electric machines. The morecycles, the shorter the life of the energy storage device.

Under certain operating conditions it is desirable to save fuel and toavoid cooling of the combustion engine's exhaust after treatment system,while the vehicle is driven with a desired torque.

The document EP-B1-1126987 shows a gearbox with double planetary gears.Each sun wheel of the planetary gear is connected to an electricalmachine, and the internal wheels of the planetary gears are connectedwith each other. The planetary wheel carrier in each planetary gear isconnected to a number of gear pairs, so that an infinite number of gearsteps is obtained. Another document, EP-B1-1280677, also shows how theplanetary gears may be bridged with a gear step arranged on thecombustion engine's output shaft.

The document US-A1-20050227803 shows a vehicle transmission with twoelectric machines, connected to the respective sun wheels in twoplanetary gears. The planetary gears have a common planetary wheelcarrier, which is connected to the transmission's input shaft.

The document WO2008/046185-A1 shows a hybrid transmission with twoplanetary gears, wherein one electrical machine is connected to one ofthe planetary gears and a double clutch interacts with the secondplanetary gear. Both planetary gears also interact with each other via acogwheel transmission.

SUMMARY OF THE INVENTION

Despite prior art solutions in the field, there is a need to furtherdevelop a method to control a hybrid powertrain, in order to achievegear shifts without any torque interruption and to optimize the fuelconsumption in a combustion engine arranged in the powertrain.

The objective of this invention is to provide a novel and advantageousmethod to control a hybrid powertrain, which optimizes the fuelconsumption in a combustion engine arranged in the powertrain.

Another objective of this invention is to provide a novel andadvantageous method to control a hybrid powertrain, which optimizes theexhaust after treatment in a combustion engine arranged in thepowertrain.

Another objective of the invention is to provide a novel andadvantageous computer program to control a hybrid powertrain.

With the method according to the invention, an efficient and reliablemethod to control a hybrid powertrain in order to optimize the fuelconsumption is obtained, wherein the hybrid powertrain comprises acombustion engine; a gearbox with an input shaft and an output shaft; afirst planetary gear, connected to the input shaft and a first mainshaft; a second planetary gear, connected to the first planetary gearand a second main shaft; a first electrical machine, connected to thefirst planetary gear; a second electrical machine, connected to thesecond planetary gear; at least one gear pair connected with the firstmain shaft, and therefore the first planetary gear and the output shaft;and at least one gear pair connected with the second main shaft, andtherefore with the second planetary gear and the output shaft, whereinthe combustion engine is connected with a first planetary wheel carrierarranged in the first planetary gear via the input shaft of the gearbox,and wherein the second main shaft is connected with a planetary wheelcarrier arranged in the second planetary gear.

By ensuring that the first planetary gear's moveable parts aredisconnected from each other and that the second planetary gear'smoveable parts are disconnected from each other, by bringing thecombustion engine to a predetermined engine speed, and by controllingthe first and the second electrical machines, in such a way that adesired torque is achieved in the output shaft, the fuel consumption inthe hybrid powertrain may be optimized while one and the same gear isengaged. At some low to medium high torques in the output shaft it isthus advantageous, with the same gear engaged, to unlock the planetarygear that is locked for the gear, to bring the combustion engine to apredetermined engine speed, and to control the first and the secondelectrical machines, so that the desired torque is obtained in theoutput shaft.

According to one embodiment, the predetermined engine speed correspondssubstantially to the combustion engine's idling engine speed. Thepredetermined engine speed may be a desired engine speed in a certainoperating situation. The predetermined engine speed may be within aninterval of +/−100 revolutions/min around the idling engine speed. Thepredetermined engine speed may be within an interval of +/−200revolutions/min around the idling engine speed. The predetermined enginespeed may be within an applicable interval around the idling enginespeed, or within an interval which is lower than the idling engine speedor higher than the idling engine speed. The idling engine speed may be500 revolutions/min. The idling engine speed may be 1000revolutions/min. The predetermined engine speed may be within theinterval 300-700 revolutions/min, preferably within the interval 400-600revolutions/min. Thus, the predetermined engine speed is an engine speedthat results in a reduction of fuel consumption. A low engine speed inthe combustion engine results in reduced friction losses in thepowertrain. The low engine speed also results in the air flow in thecombustion engine, and therefore in the combustion engine's exhaustafter treatment system, being reduced. This prevents the exhaust aftertreatment system from being cooled to temperatures that have a negativeimpact on the performance of the exhaust after treatment system.

Preferably, the moveable parts arranged in the first planetary gear aredisconnected by way of controlling the first and/or the secondelectrical machine in such a way that torque balance s achieved in thefirst planetary gear, wherein a first coupling device is shifted, sothat a first planetary wheel carrier, arranged in the first planetarygear, and a first sun wheel are disconnected from each other.

Preferably, the moveable parts arranged in the second planetary gear aredisconnected by way of controlling the first and/or the secondelectrical machine in such a way that torque balance is achieved in thesecond planetary gear, wherein a second coupling device is shifted, sothat a second planetary wheel carrier, arranged in the second planetarygear, and a second sun wheel are disconnected from each other.

Torque balance relates to a state where a torque acts on an internalring gear arranged in the planetary gear, representing the product ofthe torque acting on the planetary wheel carrier of the planetary gearand the gear ratio of the planetary gear, while simultaneously a torqueacts on the planetary gear's sun wheel, representing the product of thetorque acting on the planetary wheel carrier and (1-the planetary gear'sgear ratio). In the event two of the planetary gear's component parts,i.e. the sun wheel, the internal ring gear or planetary wheel carriers,are connected with a coupling device, this coupling device does nottransfer any torque between the planetary gear's parts when torquebalance prevails. Accordingly, the coupling device may easily be shiftedand the planetary gear's component parts be disconnected.

According to one embodiment, the torque desired in the output shaft is apositive torque. Where the hybrid powertrain is arranged in a vehicle,this means that the vehicle is propelled with the first and the secondelectrical machine and the combustion engine. The torque desired in theoutput shaft is any desired torque, and may thus be a torque requestedby the vehicle's driver or a torque requested by the vehicle's controlsystem. A torque requested by the driver may be determined based on, forexample, the position of the accelerator pedal according to prevalentmethods. The desired torque is suitably determined in a control deviceconnected with the hybrid powertrain. The first and the secondelectrical machines are preferably controlled based on a desired totalpower consumption of the first and the second electrical machines, andby the torque desired in the output shaft. Thus, a given torque desiredin the output shaft may be achieved with different total powerconsumptions. Preferably, the first and the second electrical machinesare controlled in such a way that the desired total power consumption isachieved having regard to the desired power in or out of an energystorage device, and the power consumption of the other electrical loads.If a certain power consumption is desired, the first and the secondelectrical machines may thus be controlled in such a way that thedesired power consumption is achieved, while simultaneously the desiredtorque in the output shaft is achieved, having regard to the performanceof the components.

According to one embodiment, the torque desired in the output shaft is anegative torque. Where the hybrid powertrain is arranged in a vehicle,this means that the vehicle decelerates. The torque desired in theoutput shaft may thus be a torque requested by the vehicle's driver, ora torque requested by the vehicle's control system. A torque desired inthe output shaft, requested by the driver, may in this case bedetermined based on the position of the brake pedal according toprevalent methods. In some cases, so-called regenerative decelerationmay also be achieved at a negative torque in the output shaft. When thefirst and the second electrical machines are controlled in order toachieve the desired negative torque in the output shaft, the combustionengine is impacted by a torque depending on the torque produced by thefirst and the second electrical machine, respectively. The first and thesecond electrical machines are preferably controlled based on the torqueacting on the combustion engine, and on the torque desired in the outputshaft. Thus, the first and the second electrical machines may becontrolled in such a way that the desired negative torque in the outputshaft is achieved, while simultaneously the combustion engine is kept inits idling engine speed, without any fuel being supplied to thecombustion engine. Torque acting on the combustion engine may bedetermined with a speed governor.

The electrical machines, which are connected to the planetary gears, maygenerate power and/or supply torque depending on the desired operatingmode. The electrical machines may also, at certain operating times,supply each other with power.

Preferably, the first main shaft and the second main shaft are connectedto a transmission device comprising a number of connectible anddisconnectable gear pairs. The gear pairs comprise cogwheels, which aremechanically lockable with and disconnectable from the countershaft.Thus, a number of fixed gear steps is obtained, which may be shiftedwithout torque interruption. The cogwheels that may be locked on thecountershaft also result in a compact construction with a highreliability and high dependability. A gear pair may thus bedisconnected, whereat the corresponding cogwheel is disconnected fromthe countershaft, and a gear pair may be connected, whereat thecorresponding cogwheel is connected to the countershaft. Alternatively,pinion gears in the gear pairs may be arranged to be lockable with anddisconnectable from the first or second main shaft.

Each of the gear pairs has a gearing, which is adapted to the vehicle'sdesired driving characteristics. The gear pair with the highest gearing,in relation to the other gear pairs, is suitably connected when thelowest gear is engaged.

Suitably, the first planetary wheel carrier in the first planetary gearis directly connected with the combustion engine via the input shaft.Alternatively, the first planetary wheel carrier is connected with thecombustion engine via a coupling device. The second planetary wheelcarrier in the second planetary gear is preferably directly connectedwith the second main shaft, and therefore with the transmission device.Thus, a hybrid powertrain is achieved, which may transfer a large torqueto the output shaft and the therewith connected driving wheels in alloperating modes, without being dependent on electric power from theenergy storage device.

The first planetary wheel carrier in the first planetary gear ispreferably connected with the second sun wheel of the second planetarygear. The first sun wheel in the first planetary gear is preferablyconnected with the first main shaft, and the second planetary wheelcarrier in the second planetary gear is preferably connected with thesecond main shaft. Thus, a transmission is obtained, which shifts gearswithout torque interruption. Alternatively, the first planetary wheelcarrier in the first planetary gear is connected with the secondinternal ring gear of the second planetary gear. Alternatively, thefirst main shaft is connected with a first internal ring gear arrangedin the first planetary gear.

With the gearbox according to the invention conventional slip clutchesbetween the combustion engine and the gearbox may be avoided.

A locking mechanism is arranged to fixedly connect the combustionengine's output shaft with the gearbox housing. Thus, the firstplanetary wheel carrier will also be locked to the gearbox housing. Bylocking the combustion engine's output shaft with the locking mechanismand the first planetary wheel carrier with the gearbox's housing, thegearbox, and thus the vehicle, becomes adapted for electric operation bythe electrical machines. The electrical machines thus emit a torque tothe output shaft of the gearbox. Alternatively, a coupling device may bearranged between the output shaft of the combustion engine and the inputshaft of the gearbox, wherein the combustion engine may be disconnectedby opening the coupling device, and thus the gearbox, and therefore thevehicle may become adapted for electrical operation by the electricmachines.

A first and second coupling device is arranged between the planetarywheel carrier and the sun wheel of the respective planetary gears. Thetask of the coupling devices is to lock the respective planetary wheelcarriers with the sun wheel. When the planetary wheel carrier and thesun wheel are connected with each other, the power from the combustionengine will pass through the planetary wheel carrier, the couplingdevice, the sun wheel and further along to the gearbox, which entailsthat the planetary wheels do not absorb any torque. This entails thatthe dimension of the planetary wheels may be adapted only to theelectrical machine's torque instead of the combustion engine's torque,which in turn means the planetary wheels may be designed with smallerdimensions. Thus, a drive arrangement according to the invention isobtained, which has a compact construction, a low weight and a lowmanufacturing cost.

The coupling devices and the locking mechanisms preferably comprise anannular sleeve, which is shifted axially between a connected and adisconnected state. The sleeve encloses, substantially concentrically,the gearbox's rotating components and is moved between the connected anddisconnected state with a power element. Thus, a compact construction isobtained, with a low weight and a low manufacturing cost.

BRIEF DESCRIPTION OF THE DRAWINGS

Below is a description, as an example, of preferred embodiments of theinvention with reference to the enclosed drawings, on which:

FIG. 1 schematically shows a vehicle in a side view with a hybridpowertrain, controlled according to the present invention,

FIG. 2 schematically shows a side view of a hybrid powertrain,controlled according to the present invention,

FIG. 3 shows a simplified schematic view of the hybrid powertrain inFIG. 2, and

FIG. 4 shows a flow chart of the method to control hybrid powertrainaccording to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 shows a schematic side view of a vehicle 1, comprising a gearbox2 and a combustion engine 4, which are comprised in a hybrid powertrain3. The combustion engine 4 is connected to the gearbox 2, and thegearbox 2 is further connected to the driving wheels 6 of the vehicle 1via a propeller shaft 9. The driving wheels 6 are equipped with brakedevices 7 to brake the vehicle 1.

FIG. 2 shows a schematic side view of a hybrid powertrain 3 with agearbox 2, comprising an input shaft 8, a first and a second planetarygear 10 and 12, respectively, a first and a second electrical machine 14and 16, respectively, a countershaft 18 and an output shaft 20. Thehybrid powertrain 3 comprises a combustion engine 4 connected to thegearbox 2. The combustion engine 4 is connected with the gearbox 2 viathe input shaft 8 of the gearbox. The combustion engine has an outputshaft 97. The output shaft 97 of the combustion engine 4 is connected tothe input shaft 8 in the gearbox 2. The first planetary gear 10 has afirst internal ring gear 22, to which a first rotor 24 in the firstelectrical machine 14 is connected. The first planetary gear 10 also hasa first sun wheel 26 and a first planetary wheel carrier 50. The firstplanetary wheel carrier 50 is connected with the combustion engine 4 viathe input shaft 8 of the gearbox. The second planetary gear 12 has asecond internal ring gear 28, to which a second rotor 30 of the secondelectrical machine 16 is connected. The second planetary gear 12 has asecond sun wheel 32 and a second planetary wheel carrier 51. The firstand the second sun wheels 26 and 32, respectively, are coaxiallyarranged, which, according to the embodiment displayed, entails that afirst main shaft 34 arranged on the first sun wheel 26 extends inside asecond main shaft 36, which is equipped with a central boring 38,arranged on the second planetary wheel carrier 51. It is also possibleto arrange the first main shaft 34 in parallel with and next to thesecond main shaft 36. In this case, the countershaft 18 is suitablyarranged between the first main shaft 34 and the second main shaft 36,and the torque may be extracted directly from the countershaft 18. Thecountershaft 18 thus constitutes, in this case, the output shaft 20.

The first electrical machine 14 is equipped with a first stator 40,which is connected to the vehicle 1, via a gear housing 42 surroundingthe gearbox 2. The second electrical machine 16 is equipped with asecond stator 44, which is connected to the vehicle 1, via a gearhousing 42 surrounding the gearbox 2. The first and the secondelectrical machine 16 are connected to an energy storage device 46, suchas a battery, which, depending on the vehicle's 1 operating mode,operates the electrical machines 14 and 16, respectively. At otheroperating modes, the electrical machines 14 and 16, respectively, maywork as generators, wherein power is supplied to the energy storagedevice 46. An electronic control device 48 is connected to the energystorage device 46 and controls the supply of power to the electricalmachines 14 and 16, respectively. Preferably the energy storage device46 is connected to the electrical machines 14 and 16, respectively, viaa switch 49, which is connected to the control device 48. In someoperating modes, the electrical machines 14 and 16, respectively, mayalso operate each other. Electric power is then led from one of theelectrical machines 14, 16 to the second electrical machine 14, 16 viathe switch 49, connected to the electrical machines 14, 16. Thus, it ispossible to achieve a power balance between the electrical machines 14,16. Another computer 53 may also be connected to the control device 48and the gearbox 2.

The first planetary gear 10 is equipped with a first planetary wheelcarrier 50, on which a first set of planetary wheels 52 is mounted. Thesecond planetary gear 12 is equipped with a second planetary wheelcarrier 51, on which a second set of planetary wheels 54 is mounted. Thefirst set of planetary wheels 52 interacts with the first internal ringgear 22 and the first sun wheel 26. The second set of planetary wheels54 interacts with the second internal ring gear 28 and the second sunwheel 32. The input shaft 8 of the gearbox 2 is connected with the firstplanetary wheel carrier 50.

A first coupling device 56 is arranged between the first sun wheel 26and the first planetary wheel carrier 50. By arranging the firstcoupling device 56 in such a way that the first sun wheel 26 and thefirst planetary wheel carrier 50 are connected with each other, and maytherefore not rotate in relation to each other, the first planetarywheel carrier 50 and the first sun wheel 26 will rotate with equalrotational speeds.

A second coupling device 58 is arranged between the second sun wheel 32and the second planetary wheel carrier 51. By arranging the secondcoupling device 58 in such a way that the second sun wheel 32 and thesecond planetary wheel carrier 51 are connected with each other, and maytherefore not rotate in relation to each other, the second planetarywheel carrier 51 and the first sun wheel 32 will rotate with equalrotational speeds.

Preferably, the first and second coupling devices 56, 58 comprise afirst and a second splines-equipped coupling sleeve 55 and 57,respectively, which is axially shiftable on a splines-equipped sectionon the first and second, respectively, planetary wheel carrier 50 and51, and on a splines-equipped section on the respective sun wheels 26and 32. By shifting the respective coupling sleeve 55, 57 so that thesplines-equipped sections are connected via the respective couplingsleeves 55, 57, the first planetary wheel carrier 50 and the first sunwheel 26, as well as the second planetary wheel carrier 51 and thesecond sun wheel 32, respectively, become mutually interlocked with eachother and may not rotate in relation to each other.

The first and second coupling device 56, 58 according to the embodimentdisplayed in FIG. 2 are arranged between the first sun wheel 26 and thefirst planetary wheel carrier 50, and between the second sun wheel 28and the second planetary wheel carrier 51, respectively. However, it ispossible to arrange an additional or alternative coupling device (notdisplayed) between the first internal ring gear 22 and the firstplanetary wheel carrier 50, and also to arrange an additional oralternative coupling device (not displayed) between the second internalring gear 28 and the second planetary wheel carrier 51.

The first planetary wheel carrier 50 in the first planetary gear 10 is,in this embodiment, fixedly connected with the second sun wheel 32 ofthe second planetary gear 12.

A transmission device 19, which comprises a first gear pair 60, arrangedbetween the first planetary gear 10 and the output shaft 20 is connectedto the first and the second main shaft 34, 36. The first gear pair 60comprises a first pinion gear 62 and a first cogwheel 64, which are inengagement with each other. A second gear pair 66 is arranged betweenthe second planetary gear 12 and the output shaft 20. The second gearpair 66 comprises a second pinion gear 68 and a second cogwheel 70,which are in engagement with each other. A third gear pair 72 isarranged between the first planetary gear 10 and the output shaft 20.The third gear pair 72 comprises a third pinion gear 74 and a thirdcogwheel 76, which are in engagement with each other. A fourth gear pair78 is arranged between the second planetary gear 12 and the output shaft20. The fourth gear pair 78 comprises a fourth pinion gear 80 and afourth cogwheel 82, which are in engagement with each other.

On the first main shaft 34, the first and the third pinion gears 62 and74, respectively, are arranged. The first and the third pinion gears 62and 74, respectively, are fixedly connected with the first main shaft34, so that they may not rotate in relation to the first main shaft 34.On the second main shaft 36, the second and the fourth pinion gears 68and 80, respectively, are arranged. The second and the fourth piniongears 68 and 80, respectively, are fixedly connected with the secondmain shaft 36, so that they may not rotate in relation to the secondmain shaft 36.

The countershaft 18 extends substantially in parallel with the first andthe second main shaft 34 and 36, respectively. On the countershaft 18,the first, second, third and fourth cogwheels 64, 70, 76 and 82,respectively, are mounted. The first pinion gear 62 engages with thefirst cogwheel 64, the second pinion gear 68 engages with the secondcogwheel 70, the third pinion gear 74 engages with the third cogwheel 76and the fourth pinion gear 80 engages with the fourth cogwheel 82.

The first, second, third and fourth cogwheels 64, 70, 76 and 82,respectively, may be individually locked with and released from thecountershaft 18 with the assistance of the first, second, third andfourth coupling elements 84, 86, 88 and 90, respectively. The couplingelements 84, 86, 88 and 90, respectively, preferably consist ofsplines-equipped sections on the cogwheels 64, 70, 76 and 82,respectively, and on the countershaft 18, which interact with fifth andsixth coupling sleeves 83, 85 which engage mechanically with thesplines-equipped sections of the respective first to fourth cogwheel 64,70, 76 and 82 and of the countershaft 18. The first and third couplingelements 84, 88 are preferably equipped with a common coupling sleeve83, and the second and fourth coupling elements 86, 90 are preferablyequipped with a common coupling sleeve 85. In the released state, arelative rotation may occur between the cogwheels 64, 70, 76 and 82 andof the countershaft 18. The coupling elements 84, 86, 88 and 90,respectively, may also consist of friction clutches. On the countershaft18 a fifth cogwheel 92 is also arranged, which engages with a sixthcogwheel 94, which is arranged on the output shaft 20 of the gearbox 2.

The countershaft 18 is arranged between the respective first and secondplanetary gears 10, 12 and the output shaft 20, so that the countershaft18 is connected with the output shaft 20 via a fifth gear pair 21, whichcomprises the fifth and the sixth cogwheel 92, 94. The fifth cogwheel 92is arranged so it may be connected with and disconnected from thecountershaft 18 with a fifth coupling element 93.

By disconnecting the fifth cogwheel 92, which is arranged to bedisconnectable from the countershaft 18, it is possible to transfertorque from the second planetary gear 12 to the countershaft 18 via, forexample, the second gear pair 66, and to further transfer torque fromthe countershaft 18 to the output shaft 20 via, for example, the firstgear pair 60. Thus, a number of gear steps is obtained, wherein torquefrom one of the planetary gears 10, 12 may be transferred to thecountershaft 18, and further along from the countershaft 18 to the mainshaft 34, 36 connected with the second planetary gear 10, 12, finally totransfer torque to the output shaft 20 of the gearbox 2. This presumes,however, that a coupling mechanism 96 arranged between the first mainshaft 34 and the output shaft 20 is connected, which is described inmore detail below.

The fifth cogwheel 92 may be locked to and released from thecountershaft 18 with the assistance of a fifth coupling element 93. Thecoupling element 93 preferably consists of splines-equipped sectionsadapted on the fifth cogwheel 92 and the countershaft 18, which sectionsinteract with a ninth coupling sleeve 87, which engages mechanicallywith the splines-equipped sections of the fifth cogwheel 92 and thecountershaft 18. In the released state, a relative rotation may occurbetween the fifth cogwheel 92 and the countershaft 18. The fifthcoupling element 93 may also consist of friction clutches.

Torque transfer from the input shaft 8 of the gearbox 2 to the outputshaft 20 of the gearbox 2 may occur via the first or the secondplanetary gear 10 and 12, respectively, and the countershaft 18. Thetorque transfer may also occur directly via the first planetary gear 10,whose first sun wheel 26 is connected, via the first main shaft 34, tothe output shaft 20 of the gearbox 2 via a coupling mechanism 96. Thecoupling mechanism 96 preferably comprises a splines-equipped seventhcoupling sleeve 100, which is axially shiftable on the first main shaft34 and on the splines-equipped sections of the output shaft 20. Byshifting the seventh coupling sleeve 100, so that the splines-equippedsections are connected via the seventh coupling sleeve 100, the firstmain shaft 34 becomes locked with the output shaft 20, which, whenrotating, will therefore have the same rotational speed. Bydisconnecting the fifth cogwheel 92 of the fifth gear pair 21 from thecountershaft 18, torque from the second planetary gear 12 may betransferred to the countershaft 18, and further along from thecountershaft 18 to the first main shaft 34, connected with the firstplanetary gear 10, in order finally to transfer torque via the couplingmechanism 96 to the output shaft 20 of the gearbox 2.

During operation, the gearbox 2 may in some operating modes operate sothat one of the sun wheels 26 and 32, respectively, are locked with thefirst and the second planetary wheel carrier 50 and 51, respectively,with the help of the first and the second coupling device 56 and 58,respectively. The first and the second main shaft 34 and 36,respectively, then obtain the same rotational speed as the input shaft 8of the gearbox 2, depending on which sun wheel 26 and 32, respectively,is locked with the respective planetary wheel carriers 50 and 51. One orboth of the electrical machines 14 and 16, respectively, may operate asa generator to generate electric power to the energy storage device 46.Alternatively, the electrical machine 14 and 16, respectively, mayprovide a torque injection, in order to thus increase the torque in theoutput shaft 20. At some operating times, the electrical machines 14 and16, respectively, will supply each other with electric power,independently of the energy storage device 46.

It is also possible that both the first and the second electricalmachine 14 and 16, respectively, generate power to the energy storagedevice 46. At engine braking the driver releases the accelerator pedal(not displayed) of the vehicle 1. The output shaft 20 of the gearbox 2then operates one or both electrical machines 14 and 16, respectively,while the combustion engine 4 and the electrical machines 14 and 16,respectively, engine brake. The electrical machines 14 and 16,respectively, in this case generate electric power, which is stored inthe energy storage device 46 in the vehicle 1. This operating state isreferred to as regenerative braking. In order to further reinforce theeffect of deceleration, the output shaft 97 of the combustion engine 4may be locked and therefore prevented from rotating. Thus, only one ofor both the electrical machines 14 and 16, respectively, will functionas brakes and 16 generate electric power, which is stored in the energystorage device 46. The locking of the output shaft 97 of the combustionengine 4 may also be carried out when the vehicle must accelerate byonly one or both the electrical machines 14 and 16, respectively. If thetorque of one or both of the respective electrical machines 14 and 16overcomes the torque off the combustion engine 4, and having regard tothe gearing between them, the combustion engine 4 will not be able toresist the large torque which the respective electrical machines 14 and16 generate, so that it becomes necessary to lock the output shaft 97 ofthe combustion engine's 4. The locking of the output shaft 97 of thecombustion engine 4 is preferably carried out with a locking device 102,which is arranged between the first planetary wheel carrier 50 and thegear hosing 42. By locking the first planetary wheel carrier 50 and thegear housing 42, the output shaft 97 of the combustion engine 4 willalso be locked, since the output shaft 97 of the combustion engines 4 isconnected with the first planetary wheel carrier 50 via the input shaft8 of the gearbox. The locking device 102 preferably comprises asplines-equipped eighth coupling sleeve 104, which is axially shiftableon a splines-equipped section of the first planetary wheel carrier 50,and on a splines-equipped section of the gear housing. By shifting theeight coupling sleeve 104 so that the splines-equipped sections areconnected via the coupling sleeve 104, the first planetary wheel carrier50, and therefore the output shaft 97 of the combustion engine 4 isprevented from rotating.

The control device 48 is connected to the electrical machines 14 and 16,respectively, to control the respective electrical machines 14 and 16,so that they, during certain operating times, use stored electric powerto supply driving power to the output shaft 20 of the gearbox 2, andduring other operating times use the kinetic energy of the output shaft20 of the gearbox 2 to extract and store electric power. The controldevice 48 thus detects the rotational speed and/or the torque of theoutput shaft 97 of the combustion engine 4 via sensors 98 arranged atthe electrical machines 14 and 16, respectively, and in the output shaft20 of the gearbox 2, in order thus to gather information and to controlthe electrical machines 14 and 16, respectively, to operate as electricmotors or generators. The control device 48 may be a computer withsoftware suitable for this purpose. The control device 48 also controlsthe flow of power between the energy storage device 46 and therespective stators 40 and 44 of the electrical machines 14 and 16,respectively. At times when the electrical machines 14 and 16,respectively, operate as engines, stored electric power is supplied fromthe energy storage device 46 to the respective stators 40 and 44. Attimes when the electrical machines 14 and 16 operate as generatorselectric power is supplied from the respective stators 40 and 44 to theenergy storage device 46. However, as stated above, the electricalmachines 14 and 16, respectively, may, during certain operating times,supply each other with electric power, independently of the energystorage device 46.

The first and the second coupling devices 56 and 58, respectively, thefirst, second, third, fourth and fifth coupling elements 84, 86, 88, 90and 93, respectively, the coupling mechanism 96 between the first mainshaft 34 and the output shaft 20, and the locking device 102 between thefirst planetary wheel carrier 50 and the gear housing 42, are connectedto the control device 48 via their respective coupling sleeves. Thesecomponents are preferably activated and deactivated by electric signalsfrom the control device 48. The coupling sleeves are preferably shiftedby non-displayed power elements, such as hydraulically or pneumaticallyoperated cylinders. It is also possible to shift the coupling sleeveswith electrically powered power elements.

The example embodiment in FIG. 2 shows four pinion gears 62, 68, 74 and80, respectively, and four cogwheels 64, 70, 76 and 82, respectively,and two respective planetary gears 10 and 12, with associated electricalmachines 14 and 16, respectively. However, it is possible to adapt thegearbox 2 with more or fewer pinion gears and cogwheels, and with moreplanetary gears with associated electrical machines.

Below, an up-shift from a first to a seventh gear will be described,wherein the gearbox 2 is arranged in a vehicle 1 and the vehicle ispropelled by the combustion engine 4.

The input shaft 8 of the gearbox 2 is connected to the output shaft 97of the vehicle's 1 combustion engine 4. The output shaft 20 of thegearbox 2 is connected to a driving shaft 99 in the vehicle 1. At idlingof the combustion engine 4 and when the vehicle 1 is at a standstill,the input shaft 8 of the gearbox 2 rotates at the same time as theoutput shaft 20 of the gearbox 2 is at a standstill. The locking device102 is deactivated, so that the output shaft 97 of the combustion engine4 may rotate freely. Since the input shaft 8 of the gearbox 2 rotates,the first planetary wheel carrier 50 will also rotate, which entailsthat the first set of planetary wheels 52 will rotate. Since the firstplanetary wheel carrier 50 is connected to the second sun wheel 32, thesecond sun wheel 32, and thus also the second set of planetary wheels54, will rotate. By not supplying power to the first and the secondelectrical machines 14 and 16, respectively, the first and the secondinternal rings 22 and 28, respectively, which are connected with therespective first and second rotor 24 and 30 of the electrical machines14 and 16, respectively, will rotate freely, so that no torque isabsorbed by the respective internal rings 22 and 28. The first and thesecond coupling devices 56 and 58, respectively, are disconnected andthus not actuated. Thus, no torque will be transferred from thecombustion engine 4 to the sun wheel 26 of the first planetary gear 10or to the planetary wheel carrier 51 of the second planetary gear 12.The coupling mechanism 96 between the first main shaft 34 and the outputshaft 20 is disconnected, so that the first main shaft 34 and the outputshaft 20 may rotate freely in relation to each other. Since the firstplanetary gear's sun wheel 26, the planetary wheel carrier 51 of thesecond planetary gear 12 and the output shaft 20 of the gearbox 2 are,at this stage, at a standstill, the countershaft 18 is also at astandstill. In a first step the fourth cogwheel 82 and the thirdcogwheel 76 are connected with the countershaft 18 with the assistanceof the fourth and third coupling elements 90 and 88, respectively. Thefirst cogwheel 64 and the second cogwheel 70 are disconnected from thecountershaft 18. Thus, the first cogwheel 64 and the second cogwheel 70are allowed to rotate freely in relation to the countershaft 18. Thefifth cogwheel 92 of the fifth gear pair 21 is locked on thecountershaft 18 with the assistance of the fifth coupling element 93.

In order to start the rotation of the output shaft 20 of the gearbox 2,with the objective of driving the vehicle 1, the fourth pinion gear 80and the fourth cogwheel 82 on the countershaft 18 must be brought torotate. This is achieved by making the second planetary wheel carrier 51rotate. When the second planetary wheel carrier 51 rotates, the secondmain shaft 36 will also rotate and thus the fourth pinion gear 80, whichis arranged on the second main shaft 36, also rotates. The secondplanetary wheel carrier 51 is made to rotate by controlling the secondinternal ring gear 28 with the second electrical machine 16. Byactivating the second electrical machine 16 and controlling thecombustion engine 4 to a suitable engine speed, the vehicle 1 begins tomove as the second main shaft 36 begins to rotate. When the secondplanetary wheel carrier 51 and the second sun wheel 32 achieve the samerotational speed, the second sun wheel 32 is locked with the secondplanetary wheel carrier 51 with the assistance of the second couplingdevice 58. As mentioned above, the second coupling device 58 ispreferably adapted in such a way that the second sun wheel 32 and thesecond planetary wheel carrier 51 engage mechanically with each other.Alternatively, the second coupling device 58 may be adapted as a slipbrake or a multi-plate clutch which connects, in a smooth way, thesecond sun wheel 32 with the second planetary wheel carrier 51. When thesecond sun wheel 32 is connected with the second planetary wheel carrier51, the second planetary wheel carrier 51 will rotate with the samerotational speed as the output shaft 97 of the combustion engine 4.Thus, the torque generated by the combustion engine 4 is transferred tothe output shaft 20 of the gearbox 2 via the fourth pinion gear 80, thefourth cogwheel 82 on the countershaft 18, the fifth cogwheel 92 on thecountershaft 18, and the sixth cogwheel 94 on the output shaft 20 of thegearbox 2. The vehicle 1 will thus begin to move off and be propelled bya first gear.

Each of the first, second, third and fourth gear pairs 60, 66, 72, 78has a gearing, which is adapted to the vehicle's 1 desired drivingcharacteristics. According to the example embodiment displayed in FIG.2, the fourth gear pair 78 has the highest gearing compared to thefirst, second and third gear pairs 60, 66, 72, which results in thefourth gear pair 78 being connected when the lowest gear is engaged. Thesecond gear pair 66 transfers, as does the fourth gear pair 78, torquebetween the second main shaft 36 and the countershaft 18, and couldinstead be fitted out with the highest gearing, compared with other gearpairs 60, 72, 78, which is why in such an embodiment the second gearpair 66 could be connected when the lowest gear is engaged.

When the countershaft 18 is made to rotate by the fourth cogwheel 82 onthe countershaft 18, the third cogwheel 76 on the countershaft 18 willalso rotate. Thus, the countershaft 18 operates the third cogwheel 76,which in turn operates the third pinion gear 74 on the first main shaft34. When the first main shaft 34 rotates, the first sun wheel 26 willalso rotate, and thus, depending on the rotational speed of the outputshaft 97 of the combustion engine 4 and thus the rotational speed of thefirst planetary wheel carrier 50, it will cause the first internal ringgear 22 and the first rotor 24 of the first electrical machine 14 torotate. It is thus possible to allow the first electrical machine 14 tooperate as a generator to supply power to the energy storage device 46,and/or to supply power to the second electrical machine 16. It is alsopossible for the second electrical machine 16 to be operated as agenerator. Alternatively, the first electrical machine 14 may emit atorque injection, by way of the control device 48 controlling the firstelectrical machine 14 to provide a driving torque.

In order to shift gears from the first to the second gear, the lockingbetween the second sun wheel 32 and the second planetary wheel carrier51 must cease, which is achieved by way of the first and/or the secondelectrical machine 14, 16 being controlled in such a way that torquebalance prevails in the second planetary gear 12. Subsequently, thesecond coupling device 58 is controlled, so that it disconnects thesecond sun wheel 32 and the second planetary wheel carrier 51 from eachother. The second gear is connected, by way of the control device 48controlling the combustion engine 4, so that a synchronous rotationalspeed arises between the first planetary wheel carrier 50 and the firstsun wheel 26, in order to achieve a locking between the first planetarywheel carrier 50 and the first sun wheel 26. This is achieved by way ofcontrolling the first coupling device 56 in such a way that the firstplanetary wheel carrier 50 and the first sun wheel 26 are mechanicallyconnected with each other. Alternatively, the first coupling device 56may be adapted as a slip brake or a multi-plate coupling which connects,in a smooth way, the first sun wheel 26 with the first planetary wheelcarrier 50. By synchronizing the control of the combustion engine 4 andthe second and first electrical machine 14 and 16, respectively, a softand disruption-free transition from a first to a second gear may becarried out.

The first main shaft 34 now rotates, operated by the output shaft 97 ofthe combustion engine 4, and the first main shaft 34 now operates thethird pinion gear 74. The first planetary wheel carrier 50 thus operatesthe third pinion gear 74 via the first sun wheel 26 and the first mainshaft 34. Since the third cogwheel 76 is in engagement with the thirdpinion gear 74 and is connected with the countershaft 18, the thirdcogwheel 76 will operate the countershaft 18, which in turn operates thefifth cogwheel 92 on the countershaft 18. The fifth cogwheel 92 in turnoperates the output shaft 20 of the gearbox 2 via the sixth cogwheel 94,which is arranged on the output shaft 20 of the gearbox 2. The vehicle 1is now operated with a second gear.

When the countershaft 18 is made to rotate by the third cogwheel 76, thefourth cogwheel 82 will also rotate. Thus, the countershaft 18 operatesthe fourth cogwheel 82, which in turn operates the fourth pinion gear 80on the second main shaft 36. When the second main shaft 36 rotates, thesecond planetary wheel carrier 51 will also rotate, and thus, dependingon the rotational speed of the output shaft 97 of the combustion engine4, and thus the rotational speed in the first planetary wheel carrier50, it will cause the second internal ring gear 28 and the second rotor30 of the second electrical machine 16 to rotate. It is thus possible toallow the second electrical machine 16 to operate as a generator tosupply power to the energy storage device 46, and/or to supply power tothe first electrical machine 14. The second electrical machine 16 mayalso emit a torque injection, by way of the control device 48controlling the second electrical machine 16 to provide a propulsiontorque.

In order to shift from a second gear to a third gear, the fourthcogwheel 82 on the countershaft 18 must be disconnected from thecountershaft 18 with the fourth coupling element 90, so that the fourthcogwheel 82 may rotate freely in relation to the countershaft 18.Subsequently, the countershaft 18 is connected with the second cogwheel70 on the countershaft 18 via the second coupling element 86. In orderto achieve a connection of the countershaft 18 and the second cogwheel70 on the countershaft 18, preferably the second electrical machine 16is controlled in such a way that a synchronous rotational speed arisesbetween the countershaft 18 and the second cogwheel 70 on thecountershaft 18. A synchronous rotational speed may be determined by wayof measuring the rotational speed of the second rotor 30 in the secondelectrical machine 16, and by measuring the rotational speed of theoutput shaft 20. Thus, the rotational speed in the second main shaft 36and the rotational speed in the countershaft 18 may be determined by wayof given gear ratios. The rotational speed of the respective shafts 18,36 is controlled, and when a synchronous rotational speed has arisenbetween the countershaft 18 and the second cogwheel 70, the countershaft18 and the second cogwheel 70 are connected with the assistance of thesecond coupling element 86.

In order to complete the shift from a second gear to a third gear, thelocking between the first sun wheel 26 and the first planetary wheelcarrier 50 must cease, which is achieved by way of the first and/or thesecond electrical machine 14, 16 being controlled in such a way thattorque balance is achieved in the first planetary gear 10, followingwhich the first coupling device 56 is controlled, so that it releasesthe first sun wheel 26 and the first planetary wheel carrier 50 fromeach other. Subsequently, the combustion engine 4 is controlled in sucha way that a synchronous rotational speed arises between the second sunwheel 32 and the second planetary wheel carrier 51, so that the secondcoupling device 58 may be engaged in order thus to connect the secondsun wheel 32 with the second planetary wheel carrier 51, via thecoupling sleeve 57. By synchronizing the control of the combustionengine 4 and the second and first electrical machine 14 and 16,respectively, a soft and disruption-free transition from a second to athird gear may be carried out.

The third cogwheel 76 is disconnected by controlling the firstelectrical machine 14 in such a way that a substantially zero torquestate arises between the countershaft 18 and the third cogwheel 76. Whena substantially zero torque state arises, the third cogwheel 76 isdisconnected from the countershaft 18 by controlling the third couplingelement 88, so that it releases the third cogwheel 76 from thecountershaft 18. Subsequently, the first electrical machine 14 iscontrolled in such a way that a synchronous rotational speed arisesbetween the countershaft 18 and the first cogwheel 64. When asynchronous rotational speed arises, the first cogwheel 64 is connectedto the countershaft 18 by way of controlling the first coupling element84, so that it connects the first cogwheel 64 on the countershaft 18. Asynchronous rotational speed may be determined, since the rotationalspeed of the first rotor 24 in the first electrical machine 14 ismeasured and the rotational speed of the output shaft 20 is measured,following which the rotational speeds of the shafts 18, 34 arecontrolled in such a way that a synchronous engine speed arises. Thus,the rotational speed of the first main shaft 34 and the rotational speedof the countershaft 18 may be determined by way of given gear ratios.

The second main shaft 36 now rotates with the same rotational speed asthe output shaft 97 of the combustion engine 4, and the second mainshaft 36 now operates the second pinion gear 68 via the second mainshaft 36. Since the second cogwheel 70 is in engagement with the secondpinion gear 68 and is connected with the countershaft 18, the secondcogwheel 70 will operate the countershaft 18, which in turn operates thefifth cogwheel 92 on the countershaft 18. The fifth cogwheel 92 in turnoperates the output shaft 20 of the gearbox 2 via the sixth cogwheel 94,which is arranged on the output shaft 20 of the gearbox 2. The vehicle 1is now driven in a third gear.

When the countershaft 18 is made to rotate by the second cogwheel 70 onthe countershaft 18, the first cogwheel 64 on the countershaft 18 willalso rotate. Thus, the countershaft 18 operates the first cogwheel 64,which in turn operates the first pinion gear 62 on the first main shaft34. When the first main shaft 34 rotates, the first sun wheel 26 willalso rotate, and thus, depending on the rotational speed of the outputshaft 97 of the combustion engine 4, and thus the rotational speed ofthe first planetary wheel carrier 50, it will cause the first internalring gear 22 and the first rotor 24 of the second electrical machine 16to rotate. It is thus possible to allow the first electrical machine 14operate as a generator to supply power to the energy storage device 46,and/or to supply power to the second electrical machine 16.Alternatively, the first electrical machine 14 may emit a torqueinjection, by way of the control device 48 controlling the firstelectrical machine 14 to provide a driving torque.

In order to complete a shift of gears from the third to the fourth gear,the locking between the second sun wheel 32 and the second planetarywheel carrier 51 must cease, which is achieved by way of the firstand/or the second electrical machine 14, 16 being controlled in such away that torque balance prevails in the second planetary gear 12,following which the second coupling device 58 is controlled so that itreleases the second sun wheel 32 and the second planetary wheel carrier51 from each other. A fourth gear is subsequently connected by way ofthe control device 48 controlling the combustion engine 4, in such a waythat a synchronous rotational speed arises between the first planetarywheel carrier 50 and the first sun wheel 26, in order to achieve alocking between the first planetary wheel carrier 50 and the first sunwheel 26. This is achieved by way of controlling the first couplingdevice 56 in such a way that the first planetary wheel carrier 50 andthe first sun wheel 26 are mechanically connected with each other. Bysynchronizing the control of the combustion engine 4 and the second andfirst electrical machine 14 and 16 a soft and disruption-free transitionfrom a third to a fourth gear may be carried out.

The first main shaft 34 now rotates and is operated by the output shaft97 of the combustion engine 4 and the first main shaft 34 now operatesthe first pinion gear 62. The first planetary wheel carrier 50 thusoperates the first pinion gear 62 via the first sun wheel 26 and thefirst main shaft 34. Since the first cogwheel 64 is in engagement withthe first pinion gear 62 and is connected with the countershaft 18, thefirst cogwheel 64 will operate the countershaft 18, which in turnoperates the fifth cogwheel 92 on the countershaft 18. The fifthcogwheel 92 in turn operates the output shaft 20 of the gearbox 2 viathe sixth cogwheel 94, which is arranged on the output shaft 20 of thegearbox 2. The vehicle 1 is now driven in a fourth gear.

When the countershaft 18 is made to rotate by the first cogwheel 64, thesecond cogwheel 70 will also rotate. Thus, the countershaft 18 operatesthe second cogwheel 70, which in turn operates the second pinion gear 68on the second main shaft 36. When the second main shaft 36 rotates, thesecond planetary wheel carrier 51 will also rotate, and thus, dependingon the rotational speed of the output shaft 97 of the combustion engine4, and thus the rotational speed in the first planetary wheel carrier50, it will cause the second internal ring gear 28 and the second rotor30 of the second electrical machine 16 to rotate. It is thus possible toallow the second electrical machine 16 to operate as a generator tosupply power to the energy storage device 46, and/or to supply power tothe first electrical machine 14. The second electrical machine 16 mayalso emit a torque injection, by way of the control device 48controlling the second electrical machine 16 to provide a propulsiontorque.

In order to shift gears from a fourth gear to a fifth gear, the firstcogwheel 64 must be disengaged from the countershaft 18, so that thefourth gear is disengaged. This is achieved by way of controlling thecombustion engine 4 and the first electrical machine 14, in such a waythat the first cogwheel 64 is brought to a substantially zero torquestate in relation to the countershaft 18. When a substantially zerotorque state has arisen, the first coupling element 84 is disengaged, sothat the first cogwheel 64 is disconnected from the countershaft 18.

Subsequently, the rotational speed of the first main shaft 34 issynchronized with the rotational speed of the output shaft 20, followingwhich the coupling mechanism 96 is controlled in such a way that itconnects the first main shaft 34 with the output shaft 20.

Subsequently, the combustion engine 4 and the first electrical machine14 are controlled in such a way that the propulsion torque occurs viathe first main shaft 34 and via the coupling mechanism 96, and furtheralong to the output shaft 20. By reducing the torque from the secondelectrical machine 16, the fifth coupling element 93 may be brought to asubstantially zero torque state in relation to the countershaft 18. Whena substantially zero torque state has arisen, the fifth coupling element93 is disengaged, so that the fifth cogwheel 92 of the fifth gear pair21 is disconnected from the countershaft 18.

Subsequently, with the help of the second electrical machine 16, therotational speed of the countershaft 18 is synchronized with therotational speed of the third cogwheel 76, following which the thirdcoupling element 88 is controlled in such a way that it connects thethird cogwheel 76 with the countershaft 18. When this connection hasbeen completed, the propulsion torque may be shared between thecombustion engine 4, the first electrical machine 14 and the secondelectrical machine 16. Subsequently, torque balance is created in thefirst planetary gear 10, following which the first coupling device 56disconnects the first planetary wheel carrier 50 and the first sun wheel26 from each other. Finally, the second planetary wheel carrier 51 isrotational speed synchronized with the second sun wheel 32, followingwhich the second coupling device 58 connects the second planetary wheelcarrier 51 and the second sun wheel 32 with each other.

The second main shaft 36 now rotates, operated by the output shaft 97 ofthe combustion engine 4, and the second main shaft 36 operates thesecond pinion gear 68. Since the second cogwheel 70 is in engagementwith the second pinion gear 68 and is connected with the countershaft 18via the second coupling element 86, the second cogwheel 70 will operatethe countershaft 18, which in turn operates the third cogwheel 76 on thecountershaft 18. The third cogwheel 76 in turn operates the first mainshaft 34 via the third pinion gear 74, and the output shaft 20 of thegearbox 2 is thus operated via the coupling mechanism 96, which connectsthe first main shaft 34 and the output shaft 20 of the gearbox 2. Thevehicle 1 is now driven in a fifth gear.

In order to shift gears from the fifth to the sixth gear, the lockingbetween the second sun wheel 32 and the second planetary wheel carrier51 must cease, which is achieved by way of the first and/or the secondelectrical machine 14, 16 being controlled in such a way that torquebalance is achieved in the second planetary gear 12, following which thesecond coupling device 58 is controlled so that it releases the secondsun wheel 32 and the second planetary wheel carrier 51 from each other.A sixth gear is subsequently connected by way of the control device 48controlling the combustion engine 4, in such a way that a synchronousengine speed arises between the first planetary wheel carrier 50 and thefirst sun wheel 26, in order to achieve a locking between the firstplanetary wheel carrier 50 and the first sun wheel 26. This is achievedby way of controlling the first coupling device 56 in such a way thatthe first planetary wheel carrier 50 and the first sun wheel 26 aremechanically connected with each other. By synchronizing the control ofthe combustion engine 4 and the second and first electrical machine 14and 16, respectively, a soft and disruption-free transition from a fifthto a sixth gear may be carried out.

The first main shaft 34 now rotates operated by the output shaft 97 ofthe combustion engine 4, whereat the first main shaft 34 operates theoutput shaft 20 of the gearbox 2 via the coupling mechanism 96, whichconnects the first main shaft 34 and the output shaft 20 of the gearbox2. The vehicle 1 is now driven in a sixth gear.

In order to shift from a sixth to a seventh gear, the third cogwheel 76on the countershaft 18 must first be disconnected from the countershaft18 with the third coupling element 88, so that the third cogwheel 76 mayrotate freely in relation to the countershaft 18. Subsequently, thecountershaft 18 is connected with the first cogwheel 64 on thecountershaft 18 via the first coupling element 84. When the countershaft18 and the first cogwheel 64 on the countershaft 18 have a synchronousrotational speed, the first coupling element 84 is controlled in such away that the first cogwheel 64 and the countershaft 18 are connected.

In order to complete the shift from a sixth gear to a seventh gear, thelocking between the first sun wheel 26 and the first planetary wheelcarrier 50 must cease, which is achieved by way of the first and/or thesecond electrical machine 14, 16 being controlled in such a way thattorque balance is achieved in the first planetary gear 10, followingwhich the first coupling device 56 is controlled, so that it releasesthe first sun wheel 26 and the first planetary wheel carrier 50 fromeach other. Subsequently, the combustion engine 4 is controlled in sucha way that a synchronous rotational speed arises between the second sunwheel 32 and the second planetary wheel carrier 51, so that the secondcoupling device 58 may be engaged in order thus to connect the secondsun wheel 32 with the second planetary wheel carrier 51, via thecoupling sleeve 57. By synchronizing the control of the combustionengine 4 and the second and first electrical machine 14 and 16,respectively, a soft and disruption-free transition from a sixth to aseventh gear may be carried out.

The second main shaft 36 now rotates with the same rotational speed asthe output shaft 97 of the combustion engine 4, and the second mainshaft 36 operates the second pinion gear 68. Since the second cogwheel70 is in engagement with the second pinion gear 68 and is connected withthe countershaft 18, the second cogwheel 70 will operate thecountershaft 18, which in turn operates the fifth cogwheel 64 on thecountershaft 18. The first cogwheel 64 in turn operates the first mainshaft 34 via the first pinion gear 62, and the output shaft 20 of thegearbox 2 is thus operated via the coupling mechanism 96, which connectsthe first main shaft 34 and the output shaft 20 of the gearbox 2. Thevehicle 1 is now driven in a seventh gear.

According to the embodiment above, the gearbox 2 comprises pinion gears62, 68, 74, 80 and cogwheels 64, 70, 76, 82 arranged on the main shafts34, 36 and the countershaft 18, respectively, to transfer rotationalspeed and torque. However, it is possible to use another type oftransmission, such as chain and belt drives, to transfer rotationalspeed and torque in the gearbox 2.

The transmission device 19 has four gear pairs 60, 66, 72, 78 accordingto the example embodiment. However, the transmission device 19 maycomprise any number of gear pairs.

As described, torque is extracted from the gearbox 2 from the outputshaft 20. It is also possible to extract torque directly from the firstor second main shaft 34, 36, or directly from the countershaft 18.Torque may also be extracted in parallel from two or all of the threeshafts 18, 34, 36 simultaneously.

FIG. 3 illustrates the hybrid powertrain 3 according to FIG. 2 in asimplified view, where some components have been excluded in theinterest of clarity. G1 in FIG. 3 consists of at least one gear pairconnected with the first main shaft 34 and therefore with the firstplanetary gear 10, and a gear pair G2 consists of at least one gear pairconnected with the second main shaft 36 and therefore with the secondplanetary gear 12. These gear pairs G1, G2 are also connected to theoutput shaft 20. These gear pairs G1, G2 are suitably connected to theoutput shaft 20 via the countershaft 18. G1 and G2, respectively, mayconsist of one or several gear pairs. The gear pair G1, connected withthe first planetary gear 10, may for example consist of the first gearpair 60 and/or the third gear pair 72, as described in FIG. 2. The gearpair G2, connected with the second planetary gear 12, may for exampleconsist of the second gear pair 66 and/or the fourth gear pair 78, asdescribed in FIG. 2. Further, at least one gear pair G3, connected withthe output shaft 20 and the countershaft, 18 is displayed, which mayconsist of the fifth gear pair 21 described in FIG. 2. G3 may consist ofone or several gear pairs. Alternatively, torque may be extracteddirectly from the countershaft 18, which thus constitutes the outputshaft.

In the following, embodiments are described to control the hybridpowertrain 3 in order to optimize the fuel consumption in the hybridpowertrain 3. The hybrid powertrain 3 comprises a combustion engine 4; agearbox 2 with an input shaft 8 and an output shaft 20; a firstplanetary gear 10, connected to the input shaft 8 and a first main shaft34; a second planetary gear 12, connected to the first planetary gear 10and a second main shaft 36; a first electrical machine 14, connected tothe first planetary gear 10; a second electrical machine 16, connectedto the second planetary gear 12; at least one gear pair G1 connectedwith the first main shaft 34, and therefore with the first planetarygear 10 and the output shaft 20, and at least one gear pair G2 connectedwith the second main shaft 36, and therefore with the second planetarygear 12 and the output shaft 20, wherein the combustion engine 4 isconnected with a first planetary wheel carrier 50, arranged in the firstplanetary gear 10, via the input shaft 8 of the gearbox 2, and whereinthe second main shaft 36 is connected with a planetary wheel carrier 51,arranged in the second planetary gear 12.

A gear pair G1 connected with the first planetary gear 10 is connectedwith a countershaft 18, connected to the output shaft 20, and a gearpair G2, 78, which is connected with the second planetary gear 12, isalso connected to the countershaft 18. Thus, torque may be transferredbetween the first and the second planetary gears 10, 12, via thecountershaft 18, to the output shaft 20. Depending on which gear isengaged, a first planetary wheel carrier 50, arranged in the firstplanetary gear 10, and a first sun wheel 26 are connected, or a secondplanetary wheel carrier 51, arranged in the second planetary gear 12,and a second sun wheel 32 are connected.

In order to optimize the fuel consumption of the hybrid powertrain 3,first it is ensured that the first planetary gear's 10 moveable partsare disconnected from each other, and that the moveable parts of thesecond planetary gear 12 are disconnected from each other. The firstplanetary wheel carrier 50, arranged in the first planetary gear 10, andthe first sun wheel 26 are thus disconnected from each other, or thesecond planetary wheel carrier 51 and the second sun wheel 32 aredisconnected from each other, depending on which are connected. Thedisconnection relating to the first planetary wheel carrier and thefirst sun wheel is achieved by way of the first and/or the secondelectrical machine 14, 16 being controlled in such a way that torquebalance is achieved in the first planetary gear 10, following which thefirst coupling device 56 is shifted, so that the first planetary wheelcarrier 50 and the first sun wheel 26 are disconnected from each other.The disconnection relating to the second planetary wheel carrier 51 andthe second sun wheel 32 is achieved by way of the first and/or thesecond electrical machine 14, 16 being controlled in such a way thattorque balance is achieved in the second planetary gear 12, followingwhich the second coupling device 58 is shifted so that the secondplanetary wheel carrier 51 and the second sun wheel 32 are disconnectedfrom each other. Subsequently the combustion engine 4 is brought to apredetermined engine speed n_(ice), and the first and the secondelectrical machines 14, 16 are controlled in such a way that a desiredtorque T_(Drv) is achieved in the output shaft 20. Preferably, thepredetermined engine speed n_(ice) corresponds substantially to theidling engine speed of the combustion engine 4. The desired torqueT_(Drv) in the output shaft 20 is suitably determined in the controldevice 48. Below is a description of how, with known values for amongothers engine speed n_(ice), desired torque T_(Drv), and a requestedtotal power consumption P_(EM) of the first and second electricalmachines 14, 16, it is possible to obtain, with equations, how the firstand the second electrical machines 14, 16 should be controlled. Controlof the hybrid powertrain 3 and its component parts in order to optimizethe fuel consumption is suitably carried out by the control device 48.

In cases where the gear pair G3, connected with the countershaft 18 andthe output shaft 20, is connected and locked on the countershaft 18 anda coupling mechanism S6, 96, arranged between the first main shaft 34and the output shaft 20, is open, the torque T_(drv) desired in theoutput shaft 20 of the gearbox, also referred to as the requestedpowertrain torque, may be obtained through a combination of torque fromthe first and the second electrical machines 14, 16, according to theequation E1 below:

$\begin{matrix}{T_{Drv} = {{{- T_{{EM}\; 1}}\frac{S_{1}}{R_{1}}\frac{1}{G_{1}G_{3}}} + {T_{{EM}\; 2}\frac{S_{2} + R_{2}}{R_{2}}\frac{1}{G_{2}G_{3}}}}} & \lbrack{E1}\rbrack\end{matrix}$

where T_(EM1) is the torque emitted by the first electrical machine 14,and T_(EM2) is the torque emitted by the second electrical machine 16,S₁ is the number of cogs on the first sun wheel 26, R₁ is the number ofcogs on the first internal ring gear 22, S₂ is the number of cogs on thesecond sun wheel, and R2 is the number of cogs on the second internalring gear 28. G1 is the gear ratio between the first main shaft 34 andthe countershaft 18, G2 is the gear ratio between the second main shaft36 and the countershaft 18, and G3 is the gear ratio between thecountershaft 18 and the output shaft 20, for the selected connected gearpairs.

In cases where the gear pair G3, connected with the countershaft 18 andthe output shaft 20, is disconnected from the countershaft 18 and thecoupling mechanism S6, 96 is locked, and thus connects the first mainshaft 34 and the output shaft 20, the torque T_(drv) in the output shaft20 of the gearbox may be obtained from the equation E1′ below:

$\begin{matrix}{T_{Drv} = {{{- T_{{EM}\; 1}}\frac{S_{1}}{R_{1}}} + {T_{{EM}\; 2}\frac{S_{2} + R_{2}}{R_{2}}\frac{G_{1}}{G_{2}}}}} & \left\lbrack {E1}^{\prime} \right\rbrack\end{matrix}$

According to one embodiment, the torque T_(Drv) desired in the outputshaft 20 is a positive torque. Where the hybrid powertrain 3 is arrangedin a vehicle 1, this means that the vehicle 1 is propelled with thefirst and the second electrical machines 14, 16. The first and thesecond electrical machines 14, 16 thus jointly consume a total powerP_(EM) excluding losses, which is obtained from the equation E2 below:

$\begin{matrix}{P_{EM} = {\left( {{T_{{EM}\; 1}n_{{EM}\; 1}} + {T_{{EM}\; 2}n_{{EM}\; 2}}} \right)\frac{2\;\pi}{60}}} & \lbrack{E2}\rbrack\end{matrix}$

where n_(EM1) is the first electrical machine's 14 engine speed andn_(EM2) is the second electrical machine's 16 engine speed. The firstand the second electrical machines 14, 16 are preferably controlledbased on a requested total power consumption P_(EM), of the first andthe second electrical machines 14, 16, and the torque T_(Drv) desired inthe output shaft 20. The desired total power consumption P_(EM) issuitably a predetermined parameter. With a specified desired powerconsumption P_(EM) and a known desired torque T_(Drv) in the outputshaft 20, the two equations E1, E2 or alternatively E1′, E2′ may besolved to thus determine what torque the first and the second electricalmachine 14, 16 respectively, must be controlled to achieve.

According to one embodiment, the torque T_(Drv) desired in the outputshaft 20 is a negative torque. If the hybrid powertrain 3 is arranged ina vehicle 1, this entails that there is a request to decelerate thevehicle 1. When the first and the second electrical machines 14, 16 arecontrolled to achieve a negative torque in the output shaft 20, thecombustion engine 4 is impacted by a torque T_(FW), which may beobtained according to the equation E3 below:

$\begin{matrix}{T_{FW} = {\frac{\left( {S_{1} + R_{1}} \right)T_{{EM}\; 1}}{R_{1}} - \frac{S_{2}T_{{EM}\; 2}}{R_{2}}}} & \lbrack{E3}\rbrack\end{matrix}$

In order to make the combustion engine 4 rotate with the predeterminedengine speed n_(ice), the torque T_(FW) required to achieve said enginespeed n_(ice) is determined. The first and the second electricalmachines 14, 16 are thus preferably controlled based on the torqueT_(FW), which is to act on the combustion engine 4, and the torqueT_(Drv) desired in the output shaft 20. With a known desired torqueT_(Drv) in the output shaft 20, and a determined torque T_(FW) in thecombustion engine 4, the two equations E1, E3 may be solved in orderthus to determine the torque, which the first and the second electricalmachine 14, 16 respectively, must be controlled to achieve. In thismanner, the first and the second electrical machines 14, 16 may becontrolled in such a way that the torque T_(Drv) desired in the outputshaft 20 is achieved, while simultaneously the combustion engine 4 iskept at the predetermined engine speed n_(ice), without any fuel beingsupplied to the combustion engine 4. The torque T_(FW), which is to acton the combustion engine 4, may be determined with a speed governor 108(see FIG. 2).

FIG. 4 shows a flow chart relating to a method to control a hybridpowertrain 3, in order to optimize the fuel consumption in a combustionengine 4, arranged in the hybrid powertrain 3. The hybrid powertrain 3comprises a gearbox 2 with an input shaft 8 and an output shaft 20; afirst planetary gear 10, connected to the input shaft 8 and a first mainshaft 34; a second planetary gear 12, connected to the first planetarygear 10 and a second main shaft 36; a first electrical machine 14,connected to the first planetary gear 10; a second electrical machine16, connected to the second planetary gear 12; at least one gear pairG1, 60, 72 connected with the first main shaft 34, and therefore withthe first planetary gear 10 and the output shaft 20, and at least onegear pair G2, 66, 78 connected with the second main shaft 36, andtherefore with the second planetary gear 12 and the output shaft 20,wherein the combustion engine 4 is connected with a first planetarywheel carrier 50, arranged in the first planetary gear 10, via the inputshaft 8 of the gearbox 2, and wherein the second main shaft 36 isconnected with a planetary wheel carrier 51, arranged in the secondplanetary gear 12. A gear pair G1, 60, 72, connected with the firstplanetary gear 10 and therefore with the first main shaft 34, isconnected with the countershaft 18, which is connected with the outputshaft 20, and a gear pair G2, 66, 78 is connected with the secondplanetary gear 12 and therefore with the second main shaft 36, and isalso connected to the countershaft. Thus, torque may be transferredbetween the first and the second planetary gears 10, 12, via thecountershaft 18, to the output shaft 20. Depending on which gear isengaged, a first planetary wheel carrier 50, arranged in the firstplanetary gear 10, and a first sun wheel 26 are connected, or a secondplanetary wheel carrier 51, arranged in the second planetary gear 12,and a second sun wheel 32 are connected.

The method comprises the steps:

-   -   a) ensuring that the moveable parts 22 of the first planetary        gear 10, 26, 50 are disconnected from each other, and that the        moveable parts 28, 32, 51 of the second planetary gear 12 are        disconnected from each other;    -   b) bringing the combustion engine 4 to a predetermined engine        speed n_(ice); and    -   c) controlling the first and the second electrical machines 14,        16 in such a way that a desired torque T_(Drv) is achieved in        the output shaft 20.

Thus, the hybrid powertrain's fuel consumption may be optimized by wayof creating a stepless, extreme overdrive.

Suitably, the moveable parts 22, 26, 50 in the first planetary gear aredisconnected from each other by way of controlling the first and/or thesecond electrical machine 14, 16, in such a way that torque balance isachieved in the first planetary gear 10, wherein a first coupling device56 is shifted, so that a first planetary wheel carrier 50, arranged inthe first planetary gear 10, and a first sun wheel 26 are disconnectedfrom each other.

Suitably, the moveable parts 28, 32, 51 arranged in the second planetarygear 12 are disconnected from each other by way of controlling the firstand/or the second electrical machine 14, 16, in such a way that torquebalance is achieved in the second planetary gear 12, wherein a secondcoupling device 58 is shifted, so that a second planetary wheel carrier51, arranged in the second planetary gear 12, and a second sun wheel 32are disconnected from each other.

According to one embodiment, the predetermined engine speed n_(ice) instep b) substantially corresponds to the combustion engine's 4 idlingengine speed. The predetermined engine speed may be a desired enginespeed in a certain operating situation. The predetermined engine speedmay be within an interval of +/−100 revolutions/min around the idlingengine speed. The predetermined engine speed may be within an intervalof +/−200 revolutions/min around the idling engine speed. Thepredetermined engine speed may be within an applicable interval aroundthe idling engine speed, or within an interval which is lower than theidling engine speed or higher than the idling engine speed. The idlingengine speed may be 500 revolutions/min. The idling engine speed may be1000 revolutions/min. The predetermined engine speed may be within theinterval 300-700 revolutions/min, preferably within the interval 400-600revolutions/min. Thus, the predetermined engine speed is an engine speedthat results in a reduction of fuel consumption.

According to one embodiment of the method, the torque T_(Drv) desired inthe output shaft 20 is a positive torque. In this case, the step c)suitably comprises control of the first and the second electricalmachine 14, 16 based on a requested total power consumption P_(EM), ofthe first and the second electrical machine 14, 16. Suitably, the firstand the second electrical machines 14, 16 are also controlled based onthe torque T_(Drv), desired in the output shaft 20. The first and thesecond electrical machines 14, 16 are suitably controlled so that theyemit a torque T_(EM1) and T_(EM2), which may be determined by way ofcalculating the equations [1] and [2] or [1′] and [2], as described inFIG. 3.

According to one embodiment of the method, the torque T_(Drv) desired inthe output shaft 20 is a negative torque. In this case the step c)suitably comprises control of the first and the second electricalmachine 14, 16 based on a torque T_(FW), which is to act on thecombustion engine 4 to achieve the predetermined engine speed n_(ice).Suitably, the first and the second electrical machines 14, 16 are alsocontrolled based on the torque T_(Drv), desired in the output shaft 20.The first and the second electrical machine 14, 16 are suitablycontrolled so that they emit a torque T_(EM1) and T_(EM2), which may bedetermined by way of calculating the equations [1] and [3] described inFIG. 3.

Suitably, the torque T_(FW), which is to act on the combustion engine 4,is determined by a speed governor 108.

According to the invention, a computer program P is provided, stored inthe control device 48 and/or the computer 53, which may compriseprocedures to control the hybrid powertrain 3 according to the presentinvention.

The program P may be stored in an executable manner, or in a compressedmanner, in a memory M and/or a read/write memory R.

The invention also relates to a computer program product, comprisingprogram code stored in a medium readable by a computer, in order toperform the method steps specified above, when said program code isexecuted in the control device 48, or in another computer 53 connectedto the control device 48. Said program code may be stored in anon-volatile manner on said medium readable by a computer 53.

The components and features specified above may, within the framework ofthe invention, be combined between different embodiments specified.

The invention claimed is:
 1. A method to control a hybrid powertrain tooptimize fuel consumption, wherein such hybrid powertrain comprises acombustion engine; a gearbox with an input shaft and an output shaft; afirst planetary gear, connected to the input shaft and a first mainshaft; a second planetary gear, connected to the first planetary gearand a second main shaft; a first electrical machine, connected to thefirst planetary gear; a second electrical machine, connected to thesecond planetary gear; at least one gear pair connected with the firstmain shaft, and therefore the first planetary gear and the output shaft;and at least one gear pair connected with the second main shaft, andtherefore with the second planetary gear and the output shaft, whereinthe combustion engine is connected with a first planetary wheel carrier,arranged in the first planetary gear via the input shaft of the gearbox,and wherein the second main shaft is connected with a planetary wheelcarrier, arranged in the second planetary gear, said method comprisingthe steps: a) ensuring that moveable parts comprised in the firstplanetary gear are disconnected from each other, and that moveable partscomprised in the second planetary gear are disconnected from each other;b) bringing the combustion engine to a predetermined engine speed; andc) controlling the first and the second electrical machine in such a waythat a desired torque is achieved in the output shaft.
 2. A methodaccording to claim 1, wherein in step a) the first and/or the secondelectrical machine is controlled in such a way that torque balance isachieved in the first planetary gear, following which a first couplingdevice is shifted, so that the first planetary wheel carrier and a firstsun wheel are disconnected from each other.
 3. A method according toclaim 1, wherein in step a) the first and/or the second electricalmachine is controlled in such a way that torque balance is achieved inthe second planetary gear, following which a second coupling device isshifted, so that the second planetary wheel carrier and a second sunwheel are disconnected from each other.
 4. A method according to claim1, wherein the predetermined engine speed in step b) substantiallycorresponds to the combustion engine's idling engine speed.
 5. A methodaccording to claim 1, wherein the predetermined engine speed in step b)is between 300 and 700 revolutions/minute.
 6. A method according toclaim 1, wherein the torque desired in the output shaft in step c) is apositive torque.
 7. A method according to claim 6, wherein in step c)the first and the second electrical machines are controlled based on adetermined requested total power consumption of the first and the secondelectrical machine.
 8. A method according to claim 1, wherein the torquedesired in the output shaft in step c) is a negative torque.
 9. A methodaccording to claim 8, wherein in step c) the first and the secondelectrical machines are controlled based on a torque acting on thecombustion engine.
 10. A method according to claim 9, wherein thetorque, which acts on the combustion engine, is determined by a speedgovernor.
 11. A vehicle with a hybrid powertrain, said hybrid powertraincomprising: a combustion engine; a gearbox with an input shaft and anoutput shaft; a first planetary gear, connected to the input shaft and afirst main shaft; a second planetary gear, connected to the firstplanetary gear and a second main shaft; a first electrical machine,connected to the first planetary gear; a second electrical machine,connected to the second planetary gear; at least one gear pair connectedwith the first main shaft, and therefore with the first planetary gearand the output shaft; at least one gear pair connected with the secondmain shaft, and therefore with the second planetary gear and the outputshaft, wherein the combustion engine is connected with a first planetarywheel carrier, arranged in the first planetary gear via the input shaftof the gearbox, and wherein the second main shaft is connected with asecond planetary wheel carrier, arranged in the second planetary gear;and an electronic control device configured for: a) ensuring thatmoveable parts comprised in the first planetary gear are disconnectedfrom each other, and that moveable parts comprised in the secondplanetary gear are disconnected from each other; b) bringing thecombustion engine to a predetermined engine speed; and c) controllingthe first and the second electrical machine in such a way that a desiredtorque is achieved in the output shaft.
 12. A computer program productcomprising computer program code stored on a non-transitory computerreadable medium readable by a computer, said computer program productused to optimize fuel consumption, wherein such hybrid powertraincomprises a combustion engine; a gearbox with an input shaft and anoutput shaft; a first planetary gear, connected to the input shaft and afirst main shaft; a second planetary gear, connected to the firstplanetary gear and a second main shaft; a first electrical machine,connected to the first planetary gear; a second electrical machine,connected to the second planetary gear; at least one gear pair connectedwith the first main shaft, and therefore the first planetary gear andthe output shaft; and at least one gear pair connected with the secondmain shaft, and therefore with the second planetary gear and the outputshaft, wherein the combustion engine is connected with a first planetarywheel carrier, arranged in the first planetary gear via the input shaftof the gearbox, and wherein the second main shaft is connected with aplanetary wheel carrier, arranged in the second planetary gear, saidcomputer program code comprising computer instructions to cause one ormore computer processors to perform the operations of: a) ensuring thatmoveable parts comprised in the first planetary gear are disconnectedfrom each other, and that moveable parts comprised in the secondplanetary gear are disconnected from each other; b) bringing thecombustion engine to a predetermined engine speed; and c) controllingthe first and the second electrical machine in such a way that a desiredtorque is achieved in the output shaft.